Ann Taylor sandbox 14

The Mechanism of Trypsin
The reaction involves the nucleophilic attack of the active site Ser on the carbonyl carbon atom of the scissile peptide bond to form the tetrahedral intermediate. The histidine-H makes Ser-OH more nucleophilic. The decomposition of the tetrahedral intermediate to the acyl-enzyme intermediate through general acid catalysis by the active site Asp-polarized His (the His-H loses its H to the leaving amine); loss of the amine product and its replacement by a water molecule (new H-bond with histidine); the reversal of Step 2 to form a second tetrahedral intermediate (OH now bonded to cleaved carbonyl carbon and H bonded to histidine); and the reversal of Step 1 to yield the reaction’s carboxyl product and the active enzyme (electron pushing shoves off serine and the H-bond from His).

This PDB code is 2age.

It leaves the pancreas and is activated by endopeptidase and then is autocatalytic after that point, activating itself in the duodenum. After catalysis, the enzyme is changed and then restored to its original state by water.

The catalytic triad is His 57, Ser 195 and Asp 102.